Functional muscarinic receptor predominance may exist in some patients with affective disorders. This functional imbalance between various neurotransmitters may be manifested in depressed mood, elevated hypothalamic pituitary activity, and sleep abnormalities. We have tried two different approaches to test this hypothesis since this grant was originally funded. In the first, we used the Cholinergic REM Induction Test (CRIT), which measures the time to induce REM sleep following administration of arecoline (a muscarinic agonist) during the second NREM sleep period of the night. Our data to this time partially support our earlier findings that patients with affective disorder respond significantly faster than controls. In the second approach, we attempted to replicate the report of Nadi et al (1984) that patients with affective disorders have greater numbers of muscarinic receptors on skin fibroblasts than controls. We were unable, however, to confirm this report, and, partially as a result, Nadi's group has retracted the claim. Since the sleep abnormalities of depression (such as short REM latency, elevated REM density) may reflect central muscarinic over-activity, we propose four new studies which are intended to clarify the relationship between central cholinergic mechanisms, the basic physiological control of normal sleep, and possible pathophysiological sleep mechanisms in patients with major depressive disorders: (1) A Cholinergic Antagonist Challenge Strategy, comparing the sleep, mood, and neuroendocrine response of depressed patients and normal controls to bedtime administration of scopolamine for three nights, (2) A Cholinergic Agonist Challenge Strategy, comparing the REM sleep inducing properties of two different muscarinic agonists, arecoline and RS-86, in depressed and control subjects, (3) a basic neuroanatomical study of the cholinergic afferents to the medical pontine reticular formation, which appear to be crucial for initiating and maintaining REM sleep, and (4) a study of the sleep profile and brainstem muscarinic receptors of a genetic strain of rats (the Flinders Sensitive Line, developed by David Overstreet, Ph.D.) which have elevated numbers of muscarinic receptors in forebrain and which may be an animal model of depression.